This invention concerns a drive unit, especially for motor vehicles, of the type that includes an internal combustion engine and a waste-heat turbine unit that has an exhaust-gas turbine which is acted upon by the exhaust gases of the internal combustion engine, wherein the waste-heat turbine unit also utilizes, in addition to the kinetic energy, the thermal energy of the exhaust gases of the internal combustion engine through a superimposed work process in the exhaust-gas turbine, and wherein the waste-heat turbine unit includes a compressor, a secondary turbine and an exhaust-gas turbine, and the turbine blades of the exhaust-gas turbine are formed by hollow blades, through which the operating medium that was compressed by the compressor flows, expanding in the secondary turbine while furnishing power. This type of drive unit is disclosed in applicant's commonly assigned U.S. application Ser. No. 972,211, filed Dec. 22, 1978, now U.S. Pat. No. 4,294,074, which is hereby incorporated by reference.
In the case of the drive unit according to the above-referenced application, the kinetic energy of the exhaust gases is utilized directly by the exhaust-gas turbine, and the thermal energy of the exhaust gas is used indirectly by the exhaust-gas turbine. In this case, the utilization of the kinetic energy of the exhaust gases takes place by the exhaust gases acting upon turbine blades that have a profile having a curved mean camber line. However, it has proved to be a disadvantage that the exhaust gases that are admitted to the exhaust-gas turbine while they are pulsating at a high speed, because of the profile of the turbine blades, at a speed that is only slightly less than the entrance speed, flow out of the exhaust-gas turbine immediately after entering it. Because of this slight change of speed, only a relatively small part of the kinetic energy of the exhaust gases is used in the exhaust-gas turbine.
It is thus the principal object of the present invention to create a drive unit of the initially mentioned type wherein the degree of efficiency of the internal combustion engine is increased by a better utilization of the quantities and types of energy inherent in the exhaust gases in the exhaust-gas turbine.
According to the preferred embodiments of the invention this task is solved by the fact that the turbine blades are formed by pipes that have an at least approximately circular cross section.
In a particularly suitable embodiment of the invention, the turbine blades are formed by pipes with the same circular cross section. The turbine blades may, for example, in an evenly distributed way, be arranged on a circumference, or be evenly distributed on several circumferences of different sizes. The turbine blades of the individual circumferences are arranged so that, in a radial direction, they are at least partially staggered with respect to each other. A further improvement for the utilization of the kinetic energy of the exhaust gases is achieved when the turbine blades, at their outer circumference, have a profile that increases the flow resistance.
Among the principal advantages achieved by means of the invention is the fact that an increase of the degree of efficiency of the internal combustion engine is achieved by a better utilization of the kinetic energy of the exhaust gases in the exhaust-gas turbine, essentially only by means of changing the profile of the turbine blades of the exhaust-gas turbine. By means of these turbine blades, which can be manufactured with few expenditures in regard to functional efficiency, the construction of the exhaust-gas turbine is also simplified. Before exiting the exhaust-gas turbine, the exhaust gases enter into heat exchange with several turbine blades according to the invention, whereby because of the more intensive heat exchange than in the known exhaust-gas turbines, an increase of the efficiency of the internal combustion engine is also achieved due to a better utilization of the thermal energy of the exhaust gases in the exhaust-gas turbine.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.